B 12 Injections Specialists in San Antonio, TX Optimal Vitamin B12 Dosage and Treating Deficiency Vitamin B12 Shots in Canton, MI: What You Need to Know Gym goers spending monthly on vitamin B and C injections Have a f*cking word with yourself. Both are water soluble, so don't stick around for long in your system (12 14hrs) hence How often should vitamin B12 injections be administered and how frequently should laboratory monitoring be performed?